The present invention relates in general to optical devices and in particular to package assemblies for optical devices and methods for production thereof.
Optical devices include optical transmitters, optical receivers and optical systems which combine the optical transmitters and receivers. Typically, optical receivers such as imageable photodetector devices comprise a photosensitive device in a clear plastic ball grid array (PBGA) package and require ambient or artificial light sources to obtain an image. Optical receivers are used in a wide range of electronic applications including bar code readers, target recognition systems and night vision systems. In bar code readers, for example, a laser and a photodetector work together to "read" the bar code. The laser is scanned across the bar code and its reflection is received by a photodetector. The photodetector generates a digital signal representation of the bar code. The alignment between the laser, the bar code, and the photodetector is critical for accurate "reading" of the bar code. Yet, discrete optical devices such as lasers and photodetectors are conventionally not packaged together and, when combined together to form an optical system, alignment of the two discrete optical devices is exacting.
Laser diodes such as vertical-cavity surface emitting lasers (VCSELs) are also used in a wide range of electronic applications including compact disc players and drives, bar code readers, and other similar identification and data storage technologies. Laser diodes are typically side-emitting lasers that are mounted in special metal cans having a clear lens in the top of the can. There are several industry standard metal cans for these applications, for example the TO-46 and TO-56 metal cans. Because side-emitting lasers generate significant heat and degrade if overheated, metal cans like the above provide sufficient heat dissipation during operation. Typically, the metal can is mounted to a header, a laser die is mounted on a post that rises vertically above the header, and a lens is mounted separately on top of the metal can. The resulting package is often not hermetic.
These conventional laser diode packages suffer from several disadvantages including high manufacturing costs due to the need for a special mounting header and metal can. Further, with these metal can packages, critical optical alignment of the laser diode and the package is required at the time of manufacturing an optical system, at which time the metal can package must be mated to another optical component, such as an optical tube containing lenses. Alignment at this point in manufacture is critical because tolerances are as small as 10 microns. As a result of this critical alignment and tight tolerance, automatic manufacture is impossible and yield losses are significant.
Accordingly, there is a need for improved optical system packaging that has reduced manufacturing cost and improved yields, that does not require critical post-manufacturing alignment for cooperative operation between photodetectors and lasers, and that permits automated manufacturing and packaging of the optical system.